Transmission circuits



Patented June 3, 1941 TRANSMISSION CIRCUITS Christopher Dering Colchester, Sanderstead,

Surrey, England, assignor to Radio Corporation of America, a corporation of Delaware Application July 11, 1939, Serial No. 282,570 In Great Britain June .13, 1938 7 Claims.

This invention relates to transformer arrangements and has for its object to: provide improved transformer arrangements adapted in operation to give a substantially level response with a minimum of phase distortion over a wide range of signals, e. g. a range of video signals as employed in television.

Great difficulties have been experienced hitherto with transformer arrangements in obtaining level response and relativefreedom of phase distortion over a very wide range of frequencies, such as a video signal range. At the upper frequency end of such a range, where the winding impedance of a transformer is much greater than the effective impedance of its terminations, the response falls away due to the efiect of leakage impedance. On the other hand, at the lower frequency end of the range, where the leakage reactance is much less than the terminating impedance, the response is determined by the shunt effect of the winding inductances.

According to this invention a transformer coupling arrangement suitable for use over a wide range of frequencies-for example a video rangecomprises in combination two or more transformers connected in series or in parallel (or, if there be more than two transformers, they may be connected in series or in parallel or in series parallel) and condensers associated with the winding of at least one transformer, the transformers and associated condensers being so proportioned that the response is substantially level from a frequency below which the winding impedance of one transformer is too small to a frequency above which the leakage reactance of a second transformer is too large. Preferably there is provided also a phase equalizer network designed to correct for phase distortion introduced by the transformer arrangement.

The invention is illustrated in the drawing accompanying the specification in which Figures 1, 2, and 6 show diagrammatically, possible transformer arrangements for use in carrying out the invention, and Figures 3 and 4 show diagrammatically two possible equalizer networks for use in carrying out the invention, while Fig. 7 shows graphically the frequency response of the transformers and condensers.

The accompanying drawing, which is numbered Fig. 7 shows results obtained with a network as shown in Fig. 1. In Fig. 7 values of frequency in cycles per second (c./s.) kilocycles per second (kc./s.) and megacycles per second (mc./s.) are plotted. against with reference to that at 1 kc./s.

urement between 600 ohm terminations. The ac companying drawing also includes two further figures, numbered respectively 5 and 6, which show further embodiments.

In Figs. 1, 2, 3, and 4, T and '1 generally designate transformers; L and L are the primary and secondary windings of the transformers T and T respectively; K and K represent the coupling co-eflicients of the transformers T and T respectively; C are shunt condensers across the windings of the transformer T in. Fig. 1; C are condensers in series with the windings of the transformer 'I in Fig. 2; and the remaining references designate inductances or capacities, references containing the letter L being inductances, and those containing the letter C capacities. In the mathematical analysis to be given later here in, the same references are used also to designate the quantitative values of the elements to which they refer, e. g. in the mathematical analysis L represents the value of the inductance of the winding L In Fig. 1 the two transformers are in series with shunt condensers C across the windings L and. in Fig. 2 the two transformers are in parallel with the condensers C in series with the windings L Consider first the arrangement of Fig. 1 and for the sake of simplicity assume that the transformer arrangement is of unity ratio working between sending and receiving impedances R0. Neglect the winding capacity and losses. Then at frequency where wLi Ro and when [tr-#1, the Z-matrix of transformer I in conjunction with the condenser C1 is and when 702% 1, the Z-matrix of transformer T2 is The Z-matrix for the combined circuit is obtained by adding these matrices and from it the ratio, which is the insertion ratio of the currents The curve of Fig. 7 was obtained by actual measin the load Rois obtained.

2 2 2 2 4 Weew t r a If now C1L1(1-kf), L2 be so proportioned that The phase shift through combination is given by the transformer tan Another form of equalizer network which can be used for the same purposes is shown m Figure 4. This network is dimensioned as follows:

The transformers need not be in series and similar results are obtainable by connecting the said transformers in parallel, as shown in Fig. 2, the same values being required for the condensers and the same relation holding between the leakage inductance of transformer T and the nductance of transformer T as in the case of Fig. l.

The above result will hold true irrespective of the actual terminating impedances of the transformers, R becoming a design impedance and the response in the region considered being effected only by mis-match between sending and receiving impedances.

The transformer combination may be of any ratio desired, the impedance of all those components on one side of the transformer being 1ncreased by the required impedance ratio. I

The transformer combination may be made balanced with respect to earth, if required, and is thus particularly useful when it is desired to connect a balanced transmission line to an unbalanced amplifier, or vice versa.

The invention is not limited to the use of chi two transformers for any number of transformers may be connected together in any of the ways described or in combinations thereof, the equalizer being made either in several sections or composed of a greater number of elements in each arm. Thus there is practically no limit. to the frequency range for level response that can be obtained between two constant impedances.

The arrangement of Fig. l is somewhat to be preferred to that of Figure 2, since in the former case the capacities of the windings of transformer V l-insofar as these capacities may be regarded as lumped capacities in shunt across the respective windings-can be absorbed in the condensers C Figure '7 shows an example of practical results obtained. The slight irregularity in the neighborhood of 30 kc./s. is due to slight errors in the values of the component used and to the absence of correction for transformer losses.

Losses in the transformers will, of course, introduce departures from the ideal level response envisaged in the foregoing mathematical analysis. Departures, due to such losses, from the theoretical ideal may be avoided at the expense of a constant loss throughout the system by making the ratio R/L for the leakage inductance of transformer T and the winding inductance of transformer T equal to the ratio G/C for the condensers. Similar practice is, of course, well known in the equalizer art.

Figures 5 and 6 show further wide band transformer networks in accordance with this invention. For the network of Fig. 5 the conditions to be satisfied are:

For the network of Figure 6 the conditions to be fulfilled are:

Phase equalizers like those already described may be used for the net works of Figs. 5 and 6. In general the networks of Figs. 5 and 6 will not give so wide aresponse band as those previously described since they call for a smaller ratio of leakage inductance of one transformer to inductance of the other.

Having described my invention, what I claim 1s:

1. An electrical energy transfer system comprising a plurality of transformers having their primary windings inter-connected and their secondary windings inter-connected, one of the plurality of said transformers having a primary winding whose inductance is substantially equal to one-fourth of the primary winding of another of said transformers multiplied by a factor of 1k: where k; is the coupling coefficient between the primary and secondary windings of said first named transformer, a condenser connected across at least one of the primary windings, a condenser connected across at least one of the secondary windings, said condensers being so proportioned as to provide substantially constant amplitude of transfer energy between .a predetermined minimum frequency and a predetermined maximum frequency, and a phase correcting network connected across the interconnected secondary windings of -the.transformers.

2. An electrical energy transfer system having a predetermined substantially constant :input and output impedance, comprising a transformer having a winding impedance substantially equal to said input impedance at a predetermined frequency, a transformer having a leakage impedanc substantially equal to said input impedance at a predetermined frequency different from the first named predetermined frequency, interconnections between the primary windings of said transformers, inter-connections between the secondary windings of said transformers, a condenser connected across at least one of the primaries of said transformers, the inductance of the primary winding across which the condenser is connected having a value substantially equal to four times the inductance of the primary winding of another one of the transformers divided by lic where k is the coupling coeflicient of the transformer across whose primary the condenser is connected, a condenser connected across at least one of said secondaries of said transformers, said condensers being so proportioned to provide substantially uniform response between the first named and second named pre-- determined frequencies, and a phase corrected network connected across the inter-connected secondaries.

3. An electrical energy transfer system having a predetermined substantially constant input and output impedance, comprising a transformer having a Winding impedance substantially equal to said input impedance at a predetermined frequency, a transformer having a leakage impedance substantially equal to said input impedance at a predetermined frequency different from the first named predetermined frequency, interconnections between th primary windings of said transformers, inter-connections between the secondary windings of said transformers, a condenser connected across at least one of the primaries of said transformers, the inductance of the primary winding across which the condenser is connected having a value substantially equal to four times the inductance of the primary winding of another one of the transformers divided by 1k where k is the coupling coefficient of the transformer across whose primary the condenser is connected, and a condenser connected across at least one of said secondaries of said transformers, said condensers being so proportioned to provide substantially uniform response between the first named and second named predetermined frequencies.

4. An electrical energy transfer system having a predetermined substantially constant input and output impedance, comprising a transformer having a winding impedance substantially equal to said input impedance at a predetermined frequency, a transformer having a leakage impedance substantially equal to said input impedance at a predetermined frequency different from the first named predetermined frequency, a series connection between the primary windings of said transformers, a series connection between the secondary windings of said transformers, a condenser connected across at least one of the primaries of said transformers, the inductance of the primary winding across which the condenser is connected having a value substantially equal to four times the inductance of the primary winding of another one of the transformers divided by 1-k where I is the coupling coefficient of the transformer across whose primary the condenser is connected, a condenser connected across at least one of the secondaries of said transformers, said condensers being so proportioned to provide substantially uniform response between the first named and second named predetermined frequencies, and a phase corrected network connected across the inter-connected secondaries.

5. An electrical energy transfer system having a predetermined substantially constant input and output impedance, comprising a transformer having a winding impedance substantially equal to said input impedance at a predetermined frequency, a transformer having a leakage impedance substantially equal to said input impedance at a predetermined frequency different from the first named predetermined frequency, a parallel connection between the primary windings of said transformers, a parallel connection between the secondary windings of said transformers, a condenser connected across at least one of the primaries of said transformers, the inductance of the primary winding across which the condenser is connected having a value substantially equal to four times the inductance of the primary winding of another one of the transformers divided by 1lc where k is the coupling coefficient of the transformer across whose primary the condenser is connected, a condenser connected across at least one of the secondaries of said transformers, said condensers being so proportioned to provide substantially uniform response between the first named and second named predetermined frequencies, and a phase corrected network connected across the inter-connected secondaries.

6. An electrical energy transfer system having a predetermined substantially constant input and output impedance, comprising a transformer having a winding impedance substantially equal to said input impedance at a predetermined frequency, a transformer having a leakage impedance substantially equal to said input impedance at a predetermined frequency different from the first named predetermined frequency, a series connection between the primary windings of said transformers, a series connection between the secondary windings of said transformers, a condenser connected across at least one of the primaries. of said transformers, the inductance of the primary winding across which the condenser is connected having a value substantially equal to four times the inductance of the primary winding of another one of the transformers divided by 1-10 where k is the coupling coefficient of the transformer across whose primary the condenser is connected, and a condenser connected across at least one of the secondaries of said transformers, said condensers being so proportioned to provide substantially uniform response between the first named and second named predetermined frequencies.

'7. An electrical energy transfer system having a predetermined substantially constant input and output impedance, comprising a transformer having a winding impedance substantially equal to said input impedance at a predetermined frequency, a transformer having a leakage impedance substantially equal to said inpue impedance at a predetermined frequency difierent from the first named predetermined frequency, a parallel connection between the primary windings of said transformers, a parallel connection between the secondary windings of said transformers, a condenser connected across at least one of the primaries of said transformers, the inductance of the primary winding across which the condenser is connected having a value substantially equal to four times the inductance of the primary winding of another one of the transformers divided by 1-70 where k is the coupling coefficient of the transformer across whose primary the condenser is connected, and a condenser connected at least one of the secondaries of said transformers, said condensers being so proportioned to provide substantially uniform response between the first named and second named predetermined frequencies.

CHRISTOPHER DERING COLCHESTER. 

